Volvocina.'] iNFUsoRrAi animalcules. 151 



and au oblique notch in front, from wliich the two filaments proceed ; 

 movement vacillating, circular. Length 1-1 300th. The projecting 

 filament is three times, and the floating one about twice as long as 

 the body. (P. 21. f. 8.) 



Genus Plceotia, (D.) — Body diaphanous, having several ribs or 

 longitudinal ridges at the middle, and a circular translucent margin, 

 giving the whole a navicular form ; two locomotive filaments proceed 

 from one end. 



This distinct form of Infusoria might be mistaken for one of the 

 BaciMaria, were not the filaments clearly visible. The characters 

 of the filaments are similar to those of Anisonema, one extending 

 forwards with an undulatory movement, the other trailing and 

 capable of suddenly arresting the movement of the body by its 

 adhesion and j»ower of retraction. 



P. vitrea. — Body hyaline, with 3-4 longitudinal salient Hnes at 

 the centre, and some granules. Length 1-1 30th; movement slow. 

 Found in sea water, kept for two months. (P. 21. f. 10. a.h.) 



Genus Oxyrrhis, (D.) — Body ovoid, oblong, obliquely notched in 

 front, and prolonged into a point, several flagelliform filaments pro- 

 ceed laterally from the bottom of the fissure. 



The name indicates its elongated apex ; one species only is de- 

 scribed ; these Infusoria being but imperfectly known. 



0. marina. — Body colourless ; sub-cylindrical rugose, rounded 

 posteriorly. Length 1 -520th. (P. 21. f. 9. a. b.) Found in the 

 Mediterranean. 



Family.— VOLVOCIN"A. 



This family derives its name from the rolling motion with which 

 the extraordinary creatures belonging to it make their way through 

 theii- natural element — the water. The mode in which they self- 

 divide, whilst pent up within their loricated vestment, is a curious 

 characteristic of the family, and such as would almost warrant the 

 supposition that they hold some very near relationship to those re- 

 markable creatures termed Zoophytes. They resemble the Monads in 

 most particulars relating to their organization. The body is unvarying, 

 and except cilia, destitute of appendages. They have several digestive 

 sacs, but no true alimentary canal. Whilst propagation by self-division 



